How do you download 1.0.10a

[Jessedude2012]

please tell how to download i am sooo exited for bibliocraft 

[Loader]

On the left of the launcher, underneath the b-team menu icon, you'll see a cog.  Click the cog, and you'll get the option for what version you want to run - switch it from Recommended to manual and pick 1.0.10a, or switch it to Latest.

 

Bear in mind that it's not recommended to use it yet, or it'd be the recommended build.  Make sure you back everything up if you want to keep it.